The physiological disorder hyperhydricity occurs frequently in tissue culture and causes several morphological abnormalities such as thick, brittle, curled, and translucent leaves. It is well known that hyperhydric shoots are characterized by a high water content, but how this is related to the abnormalities is not clear. It was observed that water accumulated extensively in the apoplast of leaves of hyperhydric Arabidopsis seedlings and flooded apoplastic air spaces almost completely. In hyperhydric Arabidopsis seedlings, the volume of apoplastic air was reduced from 85% of the apoplast to only 15%. Similar results were obtained with hyperhydric shoots of statice. The elevated expression of hypoxia-responsive genes in hyperhydric seedlings showed that the water saturation of the apoplast decreased oxygen supply. This demonstrates a reduced gas exchange between the symplast and its surroundings, which will consequently lead to the accumulation of gases in the symplast, for example ethylene and methyl jasmonate. The impairment of gas exchange probably brings about the symptoms of hyperhydricity. Interestingly, stomatal aperture was reduced in hyperhydric plants, a previously reported response to injection of water into the apoplast. Closure of the stomata and the accumulation of water in the apoplast may be the reasons why seedlings with a low level of hyperhydricity showed improved acclimatization after planting into soil.

Gianní S., Sottile F. (2015): In vitro storage of plum germplasm by slow growth. Hort. Sci. (Prague), 42: 61-69.In this study, in vitro slow growth storage was investigated in four cultivars of two Sicilian (Southern Italy) plum species (Prunus domestica L. and Prunus cerasifera Ehrh. -two genotypes each). Established shoot cultures were preserved at 4°C in the dark in a Murashige and Skoog basal medium containing one of two different concentrations of sucrose (20 and 30 g/l) and with or without growth regulators. We tested the effects of cold storage, genotype and media on survival and re-growth capacity of explants after 3, 6, 9 and 12 months of storage. Effective minimal growth under cold conditions occurred in all four genotypes. The media composition did not affect survival, which, instead, appeared to be genotype-dependent. P. domestica genotypes survived cold storage the longest, for 12 and 9 months; instead, P. cerasifera ones remained viable for up to 6 months. All genotypes retained proliferation capacity under standard conditions and their re-growth capacity seems to be strongly genotype-dependent, closely related to their individual performance in response to the experimental condition of storage.

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